I have purchased a number of Great Courses offerings over the years. Most of them have been pretty good. My selections have been from a variety of categories including a fair number of science and mathematics classes. In areas like economics and history you are going to get a view that is similar to what you would get in college classroom so watch out for that.
Great Courses Plus is more of a subscription model where you pay a monthly or annual fee and can choose from the courses offered — The Liberty Classroom model. It has not been offered long so it is clearly imitating LC.
I signed up for GCP and have been favorably impressed with the courses offered (a good chunk of The Great Courses catalog including all new courses). Overall, I consider it reasonably good edutainment.